[Premium-Rx] SRT CR302A EJ KANB 301A

[Karl-Arne Markström]

Hello,
Congrats for getting a quite uncommon receiver classic.

You have gotten a very rare variant of the CR300, which was made for 
some commercial and diplomatic users in the
early 70's. This variant, the CR301A, lacks the ISB facility, 
otherwise it is the same as the CR302A.

The mode designations can be somewhat confusing;

A1.1 is the narrow CW mode, with 300 Hz BW, and variable BFO
A1.2 is the wide CW mode, with 800 Hz BW
F1.1 is the narrow FSK mode, with 300 Hz BW, and fixed BFO (usually 
2550 Hz center frequency)
F1.2 is the wide FSK mode, with 800 Hz BW
A2 A3 is AM with 7 kHz BW
A3AU is USB with 2700 Hz BW
A3AL is LSB with 2700 Hz BW
A3B is ISB, which is not available on this version

The 11 position switch enables the operator to check key parameters of 
the receiver:
Position 1 is AGC voltage or signal strength, which is very 
"scottish"
Position 2 is AF level for channel A
Position 3 is AF level for ISB channel B if fitted

The remaining positions are for checking operating parameters
Position labeled 1 is for checking the control voltage for the 10,5 
MHz oscillator PLL, serves also to check the fine tune function
Position labeled 2 is for checking the BFO level
Position labeled 3 is for checking the 10,5 MHz  oscillator level
Position labeled 4 is for checking the level of the interpolation loop 
oscillator
Position labeled 5 is for checking the OCXO level ( 5 MHz)
Position labeled 6 is for checking the PLL comparision oscillator 
level ( 1 kHz)
Position labeled 7 is for checking the PLL divider level ( 1 kHz)
Position labeled 8 is for checking operating voltages in the receiver 
by means of test jacks on the underside of the receiver
the yellow jack has a series resistor permitting measurements up to 15 
VDC, and the red jack permits up to 5V.

As your receiver apperars to have the high-performance Racal 8440 
black OCXO, you can expect extremely good frequency
stability.

Finally, your receiver seems to be modified by someone that did not 
like the decade settings on the original front panel.
It is probably a DIY modification, as I have not seen any such units 
anywhere.
In a way, it appears inspired by the CR304R SIGINT modification of the 
CR304A, which was made in small numbers in the mid 70's.

More information about the CR300 family can be found in Fred 
Osterman's book.

73/
Karl-Arne
SM0AOM



----Ursprungligt meddelande----
Från: zpz at gmx.de
Datum: 2013-06-24 02:02
Till: <premium-rx at mailman.qth.net>
Ärende: [Premium-Rx] SRT CR302A EJ KANB 301A

Hello All,
yesterday I received a swedish HF receiver, a SRT CR302A. (This was 
for heavy but luckless repairing of the Eddystone.) SRT means "Standard 
Radio and Telephone".
The label "302A" was hidden by a sticker saying "EJ KAN B 301A". 
A switchs allows the following modes: A1.1, A1.2 (CW), F1.1, F1.2 
(seems to be the FSK option), A2.A3 (AM), A3AU (USB), A3AL (LSB), A3B 
(DSB ?). Some more positons are possible which are not marked.

Does anybody knows about this unit? On the web there is only some very 
basic information.

There is a switch with 11 positions, going from AGC to Chan.A, Chan.B 
and numbers from 1 to 8. I am not sure what this is good for. It is not 
HF gain because manual gain control is done with a potentiometer below 
and activated with a push button.
The display consists of 6 nixie tubes in original but somebody swapped 
the 4 lower digits with big LED digits. That looks strange, but after a 
while I liked it. Then the tuning seems to be also modified. The 
original unit has a switch for each digit - you have to move to another 
switch if you want to change from i.e. 7,999.9 KHz to 8,000.0 KHz. So 
instead of a 100Hz step you can produce a step of 1 MHz. (First nulling 
the 4 lower digits and then incrementing the MHz-digit). I do not know 
if this is originally the same with every digit - on mine unit two 
switches were omitted and the 100Hz tuning knob is able to make a carry 
for 1, 10 and 100 KHz. The control of the LED digits is realized with a 
DIY pcb. 
The internal 5 MHz reference was a little surprise to me, as this 
seems to be a big OCXO. I do not know if this was usual for commercial 
receivers that time.

I fiddled around a bit with this heavy unit and found that I never 
heard CW so good at my location. The area is electromagnetically 
polluted in the sw range and I have only some indoor antenna wire. Of 
course, with wider filters I found nearly the same problems as with the 
other receivers.

b.r.
Peter


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